LEDs represent an attractive alternative to incandescent light bulbs in illumination devices due to their smaller form factor, lower energy consumption, longer operational lifetime, and enhanced mechanical robustness. To provide the aforementioned advantages, LEDs must be controlled and driven properly. In particular, in contrast to incandescent bulbs, the operating conditions (e.g., temperature) to which an LED is subjected used greatly affect the performance (e.g., luminous intensity) thereof. The operating conditions are controlled by an LED driver, typically by regulating the current flowing through the LEDs; the LED driver, however, is typically designed as general-purpose circuitry for use with a wide variety of LEDs. Accordingly, LEDs having different load characteristics may experience substantially varying operating conditions and performance despite using the same driver. In addition, because the input load characteristics of an LED do not remain constant over the LED's lifetime, but instead change with age and environmental conditions, the compatibility between an LED and its driver may erode over time, thereby causing unstable LED performance.
Conventionally, the load characteristics or operating conditions of LEDs are monitored by external circuitry that communicates the monitored information over an external data path to the LED driver. Upon detecting changes in the load characteristics or operating conditions of LEDs, for example, the external circuitry transmits a feedback signal to the LED driver to change the output load impedance or signal frequency to compensate for the changes. The external circuitry may involve, for example, a temperature-sensitive element (e.g., thermistor, thermocouple, etc.) positioned near the LEDs and a discrete data channel to communicate the sensed temperature. Such complex and specialized circuit designs can be expensive and inconveniently implemented, especially when the sensing system is far from the driver. Additionally, various schemes for communicating the LED performance information may interrupt normal operation of the LEDs.
Consequently, there is a need for circuitry that can reliably monitor the operating conditions of the LEDs without interrupting normal operation, vary the output of the LED driver to optimize the performance of the LEDs, and is conveniently deployed in a luminaire or other LED-based device.